After my first Camino with the culture shock of hitting the crowds of pilgrims with new shoes, clean clothes, and a fresh haircut in Sarria, I resolved to do just what you are suggesting next time. In the end, I did not do it (twice!), simply because that would separate you from the cohort you have walked all those previous weeks with. There is also the matter of abandoning a goal you have had fixed in your mind since you resolved to buy your plane ticket: Walking into the Cathedral Square in SdC. So I put up with the sudden influx of people on the Sarria - SdC section which really is a LOT busier than you have seen so far. As a matter of perspective, I am a fast (but not far!) walker, who usually is the last one out of an Albergue. Before Sarria, I might pass 50 people in a day. After Sarria, it was many hundreds.
The Finisterre section is fantastic, and no where near as busy as the last 100 from Sarria. Finisterre returns you to the earlier trail vibe, but is a prettier walk, and is my favorite section of the trail, and not to be missed. The truth, however, is that from a trail/beauty/walking/weather viewpoint, its all Galicia, and the two ends of what is really the same trail are very similar. One end is crowded with both pilgrims and services, and the other is not.
Can you do both? Skipping Sarria seems like something you would consider if you really did not like a busy trail, and you were running out of time, and you did not care about getting a Compostela. Do these apply to you? Only you can decide.
Buen Camino